This invention relates to a controller for regulating the volumetric rate of flow of air through a duct. More particularly, the invention relates to a controller for maintaining a substantially constant volumetric rate of flow of air under a given condition and for resetting the constant volumetric flow rate under one or more different conditions.
A controller of this general type is disclosed in Maxson et al U.S. Pat. No. 4,264,035. In that controller, a minimum volumetric flow rate is maintained under one condition. Under a different condition, a pneumatic actuator resets the controller to establish a higher volumetric flow rate. If yet a different condition exists, a second pneumatic actuator further resets the controller to establish a still higher flow rate. Thus, a controller with two pneumatic actuators is capable of responding to three different conditions.